This invention relates to mechanical seals and especially cartridge mechanical seals which use compressed packing materials and not elastomers to create secondary sealing points.
A Mechanical seal comprises a “floating” component which is mounted axially movably around the rotary shaft of, for example, a pump and a “static” component which is axially fixed, typically being secured to a housing. The floating component has a flat annular end face, i.e. its seal face, directed towards a complementary seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more spring members. In use, one of the floating and static components rotates; this component is therefore referred to as the rotary component. The other of the floating and static components does not rotate and is referred to as the stationary component.
Those seals whose floating component is rotary are described as rotary seals. If the floating component is stationary, the seal is referred to as a stationary seal.
If the sliding seal between the Rotary and Stationary components are assembled and pre-set prior to despatch from the Mechanical seal manufacturing premises, the industry terminology for this is “cartridge seal”. If the Rotary and Stationary components are despatched individually (unassembled) form the Mechanical Seal manufacturing premises, the industry terminology for this is “component seal”.
Mechanical seals often include elastomeric members to seal static and semi-dynamic surfaces. In certain seal designs such elastomeric members may be replaced with packing materials, which form a compression seal between two or more surfaces.
For the clarity of this invention the term elastomer may be thought of as on o-ring, lip seal, wiper seal or a similar component which has an elastomeric membrane or structure. Likewise, a packing material may be thought of as graphite, PTFE or a material, which may be compressed, often to change its density, to create a seal between two or more surfaces. Such materials are considered to have no, or very little elastomeric membrane.
Mechanical seals are used in all types of industries to seal a variety of different process media and operating conditions.
Such operating conditions range for high temperatures, pressures or particularly aggressive chemicals. In such cases it is imperative that the correct selection of materials, used in the mechanical seal construction, is made.
Elastomers are often the weakest link in the mechanical seal construction. This is due to the fact that they need to be chemically compatible with the sealed media and withstand various operating conditions. Furthermore, elastomers often degrade when subjected to high/low temperatures or pressures. This often limits the mechanical seal life.